1. Field of the Invention
The present invention relates to a thermally formed article comprising a sugar polymer, a production process thereof, a toner cartridge, and a recording medium, and particularly to a thermally formed article which has biodegradability and recycling ability and is excellent in flexural strength and tensile strength, a production process thereof, a toner cartridge, and a recording medium.
2. Related Background Art
Environmental pollution of the earth is actualized, and not only industrial waste but also domestic refuse requires consideration for the environment. Under such circumstances, plastic resins, which are industrial materials, are also required to be treated so as to lighten a burden imposed on the environment. Alternatively, there is a demand for development of new materials which scarcely impose a burden on the environment and can be disposed.
The conventional methods for treating waste plastics are methods comprising degrading the waste plastics into low-molecular weight products by, for example, thermal cracking or chemical decomposition, and incinerating or burying the low-molecular weight products. However, the incineration is accompanied by exhaust of carbon dioxide and hence results in a cause of warming of the earth. When halogens, sulfur and/or nitrogen elements are contained in the resins, there is a possibility that the incineration may cause air pollution due to harmful gases. When the waste plastics are buried, almost all resins now practically used remain for a long period of time as they are. Additives and the like in the resins run out during this period to cause soil pollution.
In order to cope with such problems, the development of biodegradable polymers is actively conducted as polymers which do not adversely affect the global environment and the like upon the final disposal thereof (for example, Japanese Patent Application Laid- Open No. 5-287043). Biodegradable resins are roughly classified into three types: microbially produced products, natural products derived from plants and chemically synthesized products. An example of the microbially produced products is polyester copolymer of D-3-hydroxy-butyrate and 3-hydroxyvalerate by Alcaligenes eutroplus, which is marketed under the trade name of "Biopol". These products are biodegraded by microorganisms.
Examples of the natural products include collagen, gelatin, starch, cellulose and chitosan. These products have biodegradability by themselves. Further, mixtures of starch and modified polyvinyl alcohol, cellulose esters obtained by chemically modifying cellulose, complexes of cellulose and chitosan, and the like are also known. In the chemically synthesized products, water-soluble polymers such as polyvinyl alcohol, polyethylene glycol, aliphatic polyesters such as polyethylene adipate and polycaprolactone, and the like exhibit biodegradability.
On the other hand, from the viewpoint of effective utilization of resources, it is known to reuse low-molecular weight products derived from waste plastics as raw materials for polymers. For example, polystyrene is recovered as a styrene monomer and a styrene dimer by catalytic cracking using a solid base catalyst to supply them as raw materials for repolymerization; and polyethylene terephthalate is degraded into dimethyl phthalate, ethylene glycol, terephthalic acid, etc. by a methanolysis process using methanol, a glycolysis process using ethylene glycol or a hydrolysis process using an acid or base, and these products are utilized as raw materials for polyethylene terephthalate, or other chemicals. However, in order to take out reusable components in these cases, it is necessary to fractionate and purify degradation products through many processes. As biodegradable polymers which can solve such a problem, the present applicant et al. disclosed sugar polymers, which can be biodegraded particularly by enzymolysis and permit effective reuse of the degradation products, in EP 814093A2.
Kurita et al. (Journal of Polymer Science: Polymer Chemistry Edition, 18, 365-370, 1980) describe copolymers of cellobiose with adipic acid or phthalic acid.